The invention is directed to a new process for the production of 3-oxonitriles by condensation of carboxylic acid esters with carboxylic acid nitriles as well as new 3-oxonitriles. It is known to produce 3-oxonitriles by dimerization of carboxylic acid nitriles in the presence of strong bases after saponification of the intermediately formed iminonitrile in yields of a maximum of 80% (Houben-Weyl, Vol. VII/2a, page 515). However, this process is only useful for the production of those compounds of general formula I below in which the group R.sub.1 connected to the ##STR1## group and the --CH--R.sub.2 group are the same. If different nitriles are employed there are obtained mixtures of products.
It is further known that the 3-oxonitriles can be obtained directly by condensation of carboxylic acid esters with carboxylic acid nitriles in the presence of strong bases. Strong CH-acid carboxylic acid nitriles, such as benzyl cyanide can be condensed with alcoholates. The yields are between 65 and 70%, based on the carboxylic acid ester employed.
The acylation of slightly acid aliphatic nitriles is accomplished only at elevated temperatures. Thus the yield deteriorates to 53% in the production of 2-benzoylpropionitrile because of undesired side reactions (Houben-Weyl VIII, page 573).
Furthermore, it is known that the condensation of aliphatic nitriles with carboxylic acid esters can only be carried out with finely divided sodium amide in liquid ammonia in preparative satisfactory yields (Houben-Weyl Vol. VIII, page 574, Levine J. Amer. Chem. Soc., Vol. 68, pages 760-761).
In agreement with this data the condensation of 2-methoxybenzoic acid methyl ester with acetonitrile using sodamide/liquid ammonia gives 2-methoxybenzoylacetonitrile in 84% yield, in contrast this same reaction using sodium hydride in benzene only leads to a 27.4% reaction yield. (Kawase, Bull, Chem. Soc. Japan, Vol. 35 (1962), pages 1869-1871.)
Furthermore, the reaction of ethyl propionate with acetonitrile using only 50 weight % sodium hydride is known. Thereby the sodium hydride in benzene at the boiling temperature is first treated with the acetonitrile and then the carboxylic acid ester dropped in. In this procedure there is the danger of self-condensation of the nitrile. Therefore the 3-oxonitrile is obtained in only 52% yield (Brown, Bull. Soc. Chem. France (1971), pages 2195-2203).
These yields are completely insufficient and permit no industrial scale synthesis of the 3-oxonitriles.
Further processes for the production of 3-oxonitriles are the reaction of chlorosulfonyl isocyanate with ketones and subsequent treatment of the N-chlorosulfonyl-3-oxoamide with dimethyl formamide with the setting free of the 3-oxonitrile (Synthesis) 1973, page 682), as well as the reaction of enamines with cyanogen chloride (Kuehne, J. Amer. Chem. Soc. Vol. 81 (1959), pages 5400-5404).
Both methods are very expensive preparatively and require considerable security precautions because of the dangerous nature of the materials employed. Besides the reaction yields at a maximum are 50%, so that there cannot be carried out on industrial syntheses.
There are also known special syntheses for individual 3-oxonitriles. Thus for example, pivaloylacetonitrile is obtained from pinacolone by chlorination and reaction of the monochloropinacolone with an alkali metal cyanide (German OS No. 2819264, the entire disclosure of which is hereby incorporated by reference including U.S. Pat. No. 4,062,861 mentioned therein).
This process is multistep and requires dealing with extremely toxic cyanides. Besides it is known that .alpha.-chloroketones, as represented by .alpha.-chloropinacolone are dangerous irritant materials.